Let's assume JSON supports comments, and `foo` is a JSON document with comments, what should happen here?

    JSON.stringify(JSON.parse(foo))

Presumably you'd say that it should return a plain JSON object without comments, right? However, with the current implementation this will return a JSON document that is identical to the input, modulo whitespace. This makes it easy to write tools that can, for example, increment the version number in a nodejs package.json file programatically. Doing this in a world where comments exist becomes extremely awkward or at the very least annoying, because either you have to write your own JSON parser that preserves comments, or you have to simply discard the comments when you're writing the file.

If you go with the first option, you'll inevitably run into a scenario where you have a document like this contrived example:

    {
      // this is the first ever version!
      "version": "1.0.0"
    }

And your tool goes off and increments the version number, so you end up with:

    {
      // this is the first ever version!
      "version": "2.0.0"
    }

and now your comment is a lie.

If you go with the second option, you destroy all comments whenever you write data back to the file, so they can be deemed temporary at best.

What benefit do you actually get from having comments in either scenario?

At least you can inspect the document you got with normal tools. Not so if you include comments.

And this may even encourage people into separating the data payload from the metadata, who knows?